1. Field of the Invention
The present invention refers to a filtering device comprising at least one filtering membrane, at least one counter surface opposite to the filtering membrane and at least one gap-shaped liquid space formed between the filtering membrane and the counter surface. The present invention further refers to a filtering method, in which a liquid is introduced into a liquid space formed between a filtering membrane and a counter surface, said liquid being moved relative to the filtering membrane and/or counter surface.
2. Description of Detailed Art
A device and a method comprising the above-mentioned features are known from U.S. Pat. No. 5,034,135. By means of this known prior art, a liquid to be filtered is introduced into a cylindrical annular gap, which extends between a stationary outer cylinder which forms the counter surface and a rotating filtering cylinder at which the filtering membrane is arranged. This device is in particular suitable for filtering blood to separate the components blood plasma on the one hand and blood cells on the other hand from one another. U.S. Pat. No. 5,034,135 teaches that an outwardly directed centrifugal force is generated by the rotating filtering cylinder, said centrifugal force forcing the blood cells from the membrane outwardly whereas at the same time the blood plasma is separated from the blood cells due to a trans-membrane pressure acting through the filtering membrane. The filtrate (blood plasma) generated thereby is radially guided inwardly in the filter and is continuously guided outwardly via a rotary seal arranged in the center of rotation of the filtering cylinder.
The known device is superior to conventional filtering devices in which a suspension or an emulsion is split up at a micro-porous membrane exclusively on the basis of the trans-membrane pressure into filtrate on the one hand and into concentrate on the other hand, since by the rotation of the filtering cylinder, a motion of the liquid relative to the filtering membrane is generated and thereby a clogging of the filtering pores by the solid matter or cells or emulgated droplets is prevented. The disadvantage of the known device is, however, that it is relatively voluminous. Moreover, the structure of the known device requires a relatively high constructive effort. This in particular applies for the rotary seal, which can moreover also lead to a leakage. In particular when filtering blood, the problem of a safe and reliable sealing further occurs.
It is the object of the present invention to provide an improved filtering method and an improved filtering device. In particular, it is the object of the present invention to provide a filtering device in which a clogging of the filtering pores is prevented, which requires few space and which can be manufactured in an especially simple and inexpensive manner.
To solve the above-mentioned object by means of an apparatus, the above-mentioned filtering device is developed according to the invention in that at least the filtering membrane or the counter surface are formed as a surface of a rotary body, which is substantially arranged at a right angle with respect to the axis of rotation of the rotary body. Since either the filtering membrane or the counter surface is provided at a rotary body in the filtering device according to the invention, a gap-shaped liquid space is formed between the filtering membrane and the counter surface. If desired, the filtering membrane as well as the counter surface can be formed at one rotary body each. Due to the rotary support of the filtering membrane and/or the counter surface, a relative motion of the liquid to be filtered in the gap-shaped liquid space can be effected to generate micro-whirls at the filtering surface which prevent a clogging of the filtering pores by solid matter, corpusculary particles etc. It has shown that in case of a circular relative motion between the filtering membrane and the counter surface in a circular disk-shaped gap, a macro-flow with two helically extending liquid whirls are formed, extending one above the other and having the same sense of rotation, which, however, have an opposing radial moving direction component. Accordingly, the liquid to be filtered flows helically inwards in the one liquid whirl and helically outwardly in the other liquid whirl. By this mechanism, an aimed macro-flow can be achieved in the gap-shaped liquid space, which has an advantageous effect on the filtering processes.
Since the liquid space extends in parallel to the surface of a rotary body, which is arranged substantially perpendicular to the axis of rotation of the rotary body, the filtering device according to the invention can be realized in a relatively space-saving manner at a relatively large surface compared to the known drum arrangement. The stationary arrangement of the filtering membrane is especially preferred, so that a rotary seal for discharging the filtrate from the device can be dispensed with, which is necessary and disadvantageous in the above discussed structure of the filtering device of the prior art. Thereby the constructive structure of the filtering device according to the invention is especially simplified with respect to the above-discussed prior art.
The rotary body of the filtering device according to the invention has an essentially larger radial than axial extension and is preferably formed by a disk, in particular a circular disk. The surface may be planar or structured to enhance the generation of micro-whirls. In view of an inexpensive and simple manufacture, it is preferred to form the rotary body as a planar disk. As an alternative, the disk can also for instance have a conical or a truncated conical cross section.
A filtering device that has an increased active area at an almost unchanged constructive effort can be obtained in that two opposite filtering membranes are provided between which a circular disk is rotatably supported, each forming a counter surface to the two filtering membranes. In this preferred embodiment, not only the stationary arrangement of the filtering elements leads to a constructive simplification but also the fact that both circular surfaces of the disk are used as counter surfaces.
In a further preferred embodiment of the present invention which is in particular suitable for the filtration of toxic substances or of blood or other body liquids, the rotary body is driveable in a contact-less manner. Accordingly, a shaft penetrating the housing of the filtering device and fixed with the disk for co-rotation can be dispensed with. Rather, the housing is sealed towards the outside in the area of the support of the shaft, so that an emerging, e.g. of toxic liquid, or a penetration of germs or bacterial into the liquid space is safely prevented. A rotary body is especially to be preferred for a contact-less drive, said rotary body being metallically conductive so that the drive is effected by means of magnetic induction by means of an outwardly introduced rotating magnetic field. An exchange of used up filtering devices and a coupling with the drive for the rotatably supported rotary body can therefore be carried out in a simple manner.